In signal processing, it is often necessary to amplify or integrate an input signal in order to simulate the signal or condition it in such a manner that it can be evaluated. In this case, it is occasionally necessary to carry out impedance matching during signal processing. One example of such a use is the demodulation of the ASK-modulated signal in so-called RFID technology.
For this purpose, it is necessary to track the input signal at two different speeds. To this end, the signal has hitherto been simulated using a so-called multi-stage “OTA circuit”. In the case of such an “OTA circuit”, which is also called an operational transconductance amplifier or VC-OP and is referred to below as an OTA for short, both inputs have a high impedance and the output behaves like a high-impedance current source whose current is controlled by the voltage difference at the inputs. In addition to a small offset voltage, an OTA also makes it possible to dynamically drive capacitive loads. If the output current of an OTA is supplied to a capacitor, the resulting circuit arrangement has the function of an integrator.
In order to then be able to track an input signal at two different speeds, the multi-stage OTA has hitherto been operated using two current sources of different intensity, a current source which provides a higher current being connected to the OTA in order to track the signal which changes more rapidly. On the one hand, this results in interference signals during the switching times and, on the other hand, the multi-stage OTA gives rise to a large offset.